The circulatory system of cuttlefish (family Sepiidae) has been extensively studied; however, a comprehensive anatomical reconstruction of bobtail squids (family Sepiolidae) remains limited despite their ecological and evolutionary importance within Decapodiformes. This study reconstructs the circulatory architecture of sepiolids through comparative histological analysis
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The circulatory system of cuttlefish (family Sepiidae) has been extensively studied; however, a comprehensive anatomical reconstruction of bobtail squids (family Sepiolidae) remains limited despite their ecological and evolutionary importance within Decapodiformes. This study reconstructs the circulatory architecture of sepiolids through comparative histological analysis and documents microorganisms or parasites associated with renal tissues. Two bobtail squid species,
Rossia bipapillata and
Sepiolina nipponensis, were examined using serial histological sections, while four cuttlefish species—
Sepia lycidas,
Sepia esculenta,
Sepia japonica, and
Sepia tenuipes—were analyzed for comparative purposes. Morphometric parameters, including sex, total length, and mantle length, were recorded prior to histological processing. Branchial hearts and renal appendages were sectioned using serial microtomy (~120 sections per specimen) and stained with hematoxylin and eosin, periodic acid–Schiff, Masson’s trichrome, and Giemsa to visualize vascular continuity and tissue organization. Histological observations confirmed vascular connections between the gills, branchial hearts, the systemic heart, and renal appendages, enabling reconstruction of the sepiolid circulatory pathway. In addition, the light organ characteristic of Sepiolidae was identified as a tissue receiving oxygenated blood within the circulatory network. Renal tissues revealed the presence of parasitic organisms, including
Dicyema in cuttlefish and ciliates of the genus
Chromidina in bobtail squids. Morphological observations revealed structural diversity in
Chromidina, including characteristic spiral anterior features and variation in body form, as well as developmental variation in nuclear number relative to body length in dicyemids. These findings provide new insights into cephalopod circulatory organization, parasite diversity, and host–parasite interactions.
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